This invention relates to an electrophotographic plate having high sensitivity for a long wavelength light of about 800 nm which is in a diode laser region.
Electrophotographic plates have been produced by forming a selenium (Se) film of about 50 .mu.m thick on an electroconductive substrate made of, for example, aluminum, by a vacuum deposition method. But the Se plate has a problem in that it has sensitivity only upto a wavelength of near 500 nm. On the other hand, there have been known electrophotographic plates produced by forming a Se layer of about 50 .mu.m on an electroconductive substrate, followed by the formation of a selenium-tellurium (Se-Te) alloy layer of several .mu.m thick. Such electrophotographic plates can extend the spectral light-sensitivity to a longer wavelength side by making the Te content in the Se-Te alloy higher. But with an increase of the Te adding amount, the surface charge retention properties of such electrophotographic plates become worse and cannot be used practically as an electrophotographic plate: this is a serious problem.
It is also known so-called complex double layer type electrophotographic plates produced by forming a charge generation layer on an alumium substrate by coating chlorocyan blue or squaraine derivative in about 1 .mu.m thickness, and forming a change transport layer thereon by coating a polyvinylcarbazole having high insulation resistance or a mixture of a pyrazoline derivative and polycarbonate in 10-20 .mu.m thickness. But such electrophotographic plates have practically no sensitivity to a light having a wavelength of 700 nm or more. Further, it is also known electrophotographic plates improved in the defect of the complex double layer type mentioned above so as to have sensitivity in about 800 nm which is in the diode laser region. But many of them show the longer wavelength sensitivity by forming a thin film with about 1 .mu.m film thickness of a metal phthalocyanine having one or more metals of the group III or IV of the periodic table as center metals by a vacuum deposition method, and immersing the resulting thin film in a shifting agent solution or contacting the resulting thin film with a vapor of the shifting agent so as to shift the absorption of original about 700 nm to about 800 nm. On the thus treated thin film, a charge transport layer is formed by coating a polyvinylcarbazole having high insulation resistance or a mixture of a pyrazoline derivative or a hydrazone derivative and a polycarbonate resin or polyester resin in 10-20 .mu.m thickness to produce complex double layer type electrophotographic plates. But in this case, since the metal phthalocyanine thin film having the metals of the group III or IV of the periodic table as center metals used as a charge generation layer has no absorption in the diode laser region of about 800 nm essentially, there is a serious problem in that such electrophotographic plates have no sensitivity or only low sensitivity to the light of about 800 nm (U.S. Pat. No. 4,426,434).
In laser beam printers using electrophotographic plates and laser beams as a light source, the use of diode laser as the light source has been tried variously in recent years. In this case, since the wavelength of this light source is about 800 nm, it is strongly desired to produce electrophotographic plates having high sensitivity to the longer wavelength light of about 800 nm.